Researchers at FES say no ozone emissions is optimal

A recent study by researchers led by Yale School of Forestry and Environmental Studies professor Michelle Bell and her colleagues at Johns Hopkins University has concluded that even low concentrations of ground-level ozone molecules are associated with higher mortality rates. The team examined data from 98 urban counties, covering just over 40 percent of the U.S. population.

“From a practical policy perspective, there is no safe obtainable level of ozone,” Bell said. “If there is any threshold it is at very low levels, nearing background level.”

Soon to be published in the journal Environmental Health Perspectives, the study examined whether there is a level below which ozone does not significantly affect mortality, Bell said. The study was funded primarily by the Environmental Protection Agency and also by the Centers for Disease Control.

Currently, the EPA is in the process of deciding whether to revise or retain the eight-hour ozone standard, EPA spokeswoman Suzanne Ackerman said.

This EPA standard attempts to set a safe level of ozone exposure averaged over an eight-hour period, and the agency must reconsider it every couple of years, in compliance with the Clean Air Act. The EPA will make a decision whether to change the standard by March 2007 while a final decision on the regulation will be made by December 2007, Ackerman said.

“This is an interesting study, and we will certainly look at their data as we look at all the science,” Ackerman said.

Bell said she hopes her research will help the decision-makers make an informed decision. But she also conveyed a broader message.

“Because we found no safe level of ozone, any reduction in ozone has a benefit for human health,” Bell said. “Even if [areas] meet the standards, if they lower the ozone levels there will be health benefits.”

The current paper extends previous work published in November 2004 in the Journal of the American Medical Association where Bell and her colleagues uncovered a significant association between short-term changes in ozone and mortality rates. In short, her work showed that ozone adversely affects public health.

The group uses mathematical modeling to examine the relationship between air pollution and human health. This study utilized regression to relate mortality to ozone levels and then combined data from different cities using hierarchical methods, said biostatistics professor Roger Peng, a coauthor of the paper at Johns Hopkins’ Bloomberg School of Public Health.

To study ozone levels across the entire country, the group analyzed different sets of data.

“The air pollution data was collected by the Environmental Protection Agency for regulatory purposes,” Bell said. “Weather data was collected from the National Climatic Data Center, and the mortality data is from the National Center for Health Statistics.”

By combining publicly-available data from many different cities, the researchers could pool information into a single picture of the entire nation, Peng said.